The document outlines programming in assembly language using BIOS and DOS interrupts. It discusses using INT 10H to clear the screen, set the cursor position, and other functions. It also discusses using INT 21H to input and output characters and strings to the keyboard and screen. Examples are provided to demonstrate reading a character from the keyboard, displaying it, and converting letters between upper and lower case using offsets. String instructions like MOVSB, STOS, LODS, CMPS, and SCAS are explained in relation to the SI, DI, DS, and ES registers. The use of prefixes like REP, REPE, and REPNZ with string instructions is also covered. Finally, look-up tables and

1. Chapter (4):
Bios and Dos programming in
assembly
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Chapter (4):
Outlines:
 Bios INT 10H programming: using INT 10H to:
 Clear the screen
 Set the cursor position
 others
 Dos interrupt IN 21H: using INT 21H to:
 Input character from keyboard
 Output the character to screen
 Input & output string

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 Clearing the screen using INT 10H & function 06H:

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 Setting the cursor to specific location using INT 10H & function 02H:
 Get current cursor position using INT 10H & function 03H:

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 Outputting a string of data to the monitor using INT 21H & option 09:
 Outputting a single character to the monitor using INT 21H & option 02:
 Inputting a single character using INT 21H & option 01:
 Inputting a string of data from keyboard using INT 21H & option 0A:

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 Example:
TITLE FIRST: input letter from keyboard then print letter in new raw
.MODEL SMALL
.STACK 100H
.CODE
MAIN PROC
;display the character ‘?’
MOV AH,2
MOV DL,'?'
INT 21H
;read letter from keyboard
MOV AH,01
INT 21H
MOV BL,AL ; storage letter
MOV AH,02 ; display letter
MOV DL,0DH ; carriage return
INT 21H
MOV DL,0AH ; line feed
INT 21H
; display the input letter
MOV DL,BL
INT 21H
MOV AH,4CH
INT 21H
MAIN ENDP
END MAIN

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 Example:
TITLE THIRD: CASE CONVERSION PROGRAM (from small to capital)
.MODEL SMALL
.STACK 100H
.DATA
CR EQU 0DH
LF EQU 0AH
MSG1 DB 'ENTER A LOWER CASE LETTER: $'
MSG2 DB CR,LF,'IN UPPER CASE IT IS:'
CHAR DB ?,'$'
.CODE
MAIN PROC
; initialize DS
MOV AX,@DATA
MOV DS,AX
;print user prompt
LEA DX,MSG1
MOV AH,09H
INT 21H
;input character and convert to lower case
MOV AH,01H
INT 21H
SUB AL,20H
MOV CHAR,AL
;display on the next line
LEA DX,MSG2
MOV AH,09H
INT 21H
;return to DOS
MOV AH,4CH
INT 21H
MAIN ENDP
END MAIN
MOV DX,offset MSG1
To convert from small to capital

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 Example:
In text file

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 Example:
LEA DX,MESSAGE

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 Example:

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 Example:

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 Example:

13. Chapter (5):
Macro and the Mouse
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Chapter (5):
Outlines:
 Define macro and how to use in assembly:
 How macro expanding by assembler:
 How to control the expanded of macro in list file:
 Define the local variable in macro:
 How to include the macro in another file:

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 Macro allow the programmer to write the task (set of codes perform a specific job)
once only and to invoke it whenever it is needed wherever it is needed.
 In list file the code (string message1) is expanded to:

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 Can the macro contain comments?
 The answer is yes, but there is away to suppress comments and
make the assembler show only the code only.
 If comments are preceded by (;), they will show up in the list file.
 If comments are preceded by (;;), they will not show up in the list file.
 Or using 3 directives:
 .LALL (list all): list all the instructions and the comments that are preceding
by (;) and can not list the instructions and the comments that are preceding
by (;;)
 .SALL (suppress all)
 .XALL (executable all): list only the instructions

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 Example:

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 LOCAL directive: used to define label in macro.
MULTIPLY 2,4,RESULT

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 LOCAL directive: used to define label in macro.

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 INCLUDE directive: allows a programmer to write macros and save
them in a file (for ex. “MYMACRO1.MAC”), and later bring them
into any file or program.
Include macro to clear
screen, set cursor and
display string

21. Chapter (6):
Signed Numbers & Strings &
Tables
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Lifted……

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Chapter (6):
Outlines:
 Code string instructions:
 Explain the function of registers SI & DI in string
operation
 Explain the direction flag in string instructions
 (MOVSB, MOVSW, STOS, LODS, CMPS, SCAS)
 Tables processing:
 XLAT

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 Use of SI and DI, DS and ES in string instructions:
 In 8086, the SI and DI registers always point to the source and
destination operands, respectively.
 To generate the physical address, always uses SI as the offset
of the DS register and DI as the offset of ES register.
 By using the string instructions, they are capable of compare or
transfer or … two arrays of data located in memory locations
pointed at by the SI and DI registers.

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 Byte and Word operand in string instructions:

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 Direction flag (DF) in string instructions:
 Usually, We need the pointer (incremented or decremented) to
process operands located in memory locations.
 In string operations this is achieved by the direction flag (DF).
 DF is the bit 11 (D10) in the flag register (D0 – D15).
 DF is set to high or low in order to the choice of increment or
decrement the SI and DI pointers.
 By Using the instructions:
1) CLD (clear the DF): then DF = 0, indicate the pointers should
be increment automatically (autoincrement).
2) STD (set the DF): then DF = 1, indicate the pointers should be
decrement automatically.

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 Prefix:
 REP (repeat) prefix: allow a string instruction to repeat the
operation. (process is repeated until CX = 0).
 Using the REP with string instructions MOVS, STOS, and LODS.
 REPZ (repeat zero): is the same REPE (repeat equal), will repeat
the string operation as long as the source and destination are
equal (ZF =1) or until CX = 0.
 REPNZ (repeat not zero): is the same REPNE (repeat not equal),
will repeat the string operation as long as the source and
destination are not equal (ZF =0) or until CX = 0.
 Using the REPZ & REPNZ with string instructions CMPS and
SCANS.

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 Example: (MOVSB & MOVSW)

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 STOS & LODS instructions:
 STOSB instruction: stores the byte in AL register into
memory locations pointed at by ES:DI and increment DI
once if (DF = 0), if DF = 1, then DI is decremented once.
 STOSW instruction: stores the contents of AX register into
memory locations pointed at by ES:DI and ES:DI+1 (AL into
ES:DI and AH into ES:DI+1), then increment DI twice if (DF =
0), if DF = 1, then DI is decremented twice.
 LODSB instruction: loads the content of memory locations
pointed at by DS:SI into AL and increment SI once or
decrement SI once.
 LODSW instruction: : loads the content of memory
locations pointed at by DS:SI into AL and DS:SI+1 into AH
and increment SI twice or decrement SI twice.

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 Example: (STOS & LODS )

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 CMPS & SCANS instructions:
 CMPS (compare string) instruction: allows the comparison
of two arrays of data pointed at by the SI and DI registers.
And depending on which prefix REPE or REPNE is used, a
decision is made for equality or inequality.
 SCANS (scan string) instruction: compares each byte or
word of the array of data pointed at by ES:DI with the
contents of the AL or AX. And depending on which prefix
REPE or REPNE is used, a decision is made for equality or
inequality.

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 Example: (CMPS )

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 Example: (SCANS)

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 XLAT instructions & Look-up tables:
 In some computer application, we need a table that holds
some important information or some values.
 To access the elements in the table using the XLAT
(translate) instruction.
 The table is commonly referred to a look-up table.
 To access the square value for number 5:

34. Any Question?
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